1. Technical Field
This invention relates generally to an antenna structure for use in a portable transceiver and more particularly for use in a transceiver for a portable telephone.
2. Description of the Prior Art
Portable telephones have advanced to the state where many options and features previously found only on desk-top and wall-mounted telephones are now available to a customer when he or she selects a portable telephone. As a result, some new customers are now considering a portable telephone as the primary telephone for their residences.
A typical portable telephone includes an antenna, a transmitter and a receiver for communicating a radio frequency (r-f) carrier signal that is modulated by audio signals and switching signals to and from an associated base station. In most portable telephones, both the transmitter and the receiver are active at the same time and one antenna is shared for transmission and reception. This antenna is generally a telescoping whip antenna which is extended for use and retracted or collapsed when not in use.
In view of the increased reliance on the portable telephone, one area needing improvement is that which addresses the reliability of communications between the portable telephone and the associated base station when separated by their maximum operating range. When the portable telephone is physically located at or near its maximum reception range from the base station, the antenna must be extended so that a user of the portable telephone can be assured of not missing an incoming call. Some users find the need to have the antenna extended for this condition inconvenient and therefore at times do not extend the antenna. The problem of missed calls persists, therefore, since with the antenna collapsed, the reception range of the portable telephone is typically one-third of its range with the antenna extended.
Maximum operating range for a portable telephone is obtained when the telescoping antenna is fully extended and a resonating network or loading coil, which matches to the antenna in the fully extended position, is provided. When the antenna is collapsed, however, the resonating network that matches the antenna in the extended position does not match the antenna in the collapsed position. The user of the portable telephone therefore loses somewhat more operating range than if he or she had used a non-extendible antenna that was properly matched by the resonating network.
Such a non-extendible antenna is disclosed in U.S. Pat. No. 4,721,962, issued to Heribert Gorzel on Jan. 26, 1988. This patent describes. separate transmit and receive antennas that are totally enclosed inside the housing of the portable telephone and thereby avoids any antenna parts projecting therefrom. While this antenna arrangement avoids the need to have an external antenna projecting from the portable telephone, it limits the maximum range for which the portable telephone is able to communicate with a base station simply because of the reduced antenna area available for radiating or receiving r-f energy. It is therefore. desirable to have an antenna which provides the full permitted reception and operating range when in an extended position and also the best possible operating range when in a collapsed position.